Watts AERCO Benchmark OMM-0121 Operation And Maintenance Manual page 48

Benchmark 750-3000 Boiler Operation & Maintenance Manual
SECTION 4 – MAINTENANCE
BMK 750/1000 Burner Inspection Instructions
3. Disconnect the lead wire from the flame detector installed on the burner plate. See Figure
4-4b.
4. Remove the two (2) screws securing the flame detector to the plate. The flame detector is
secured to the burner plate with one (1) #10-32 screw and one (1) #8-32 screw.
5. Remove the flame detector and gasket from the burner plate.
6. Disconnect the cable from the igniter-injector.
7. Using a 7/16" open-end wrench, disconnect the compression nut securing the gas injector
tube of the igniter-injector to the elbow of the staged ignition assembly (see Figure 4-1a).
Disconnect the staged ignition assembly from the igniter-injector.
8. Next, loosen and remove the igniter-injector from the burner plate using a 1" open-end
wrench.
9. Disconnect the unit wiring harness connectors from the air/fuel valve and blower motor.
10. Disconnect the wire leads connected to the Blower Proof switch and Blocked Inlet switch
(Figure 4-4a and Figure 4-4b).
11. Disconnect the gas train from the air/fuel valve by removing the four (4) 1/2" bolts and nuts
(Figure 4-4a).
12. Disconnect the flex hose from the air/fuel valve by loosening the hose clamp.
13. Remove the four 5/16-18 hex head screws securing the blower to the burner plate (Figure
4-4b).
14. Remove the blower and air/fuel valve from the burner plate by lifting straight up. Also,
remove the blower gasket.
15. Remove the eight (8) 3/8-16 nuts from the burner flange (Figure 4-4a) using a 9/16"
wrench.
NOTE:
The burner assembly weighs approximately 25 pounds (11.3 kg).
16. Remove the burner assembly from burner flange by pulling straight up.
17. Remove and replace the burner gasket.
NOTE:
During reassembly, apply a light coating of high-temperature, anti-seize lubricant to the
threads of the igniter-injector and grounding screw. Also, ensure that the igniter-injector is
properly positioned as indicated in Figure 4-3a. Torque the igniter-injector to 14 - 15 ft-lbs.
(19.0 - 20.3 Nm).
18. Beginning with the burner assembly removed in step 16, reinstall all the components in the
reverse order that they were removed. When reinstalling the burner flange (removed in
step 15), tighten the 3/8-16 nuts using a typical torque pattern. For example, loosely tighten
one nut, then loosely tighten a second nut on the opposite side, a third at 90 degrees to the
first two, and a fourth opposite the third, and then repeat this pattern with the remaining
four nuts. Repeat the entire pattern a second time to partially tighten all eight nuts, and
then repeat a third time until all eight nuts are fully torqued to 30 ft. lbs. (40.7 Nm).
19. Ensure that the igniter-injector and flame detector cutouts in the burner plate are properly
aligned with the heat exchanger top flange.
This completes the Benchmark 750/1000 burner inspection.
OMM-0122_D • GF-206 • 5/9/2019 Technical Support • (800) 526-0288 • Mon-Fri, 8 am - 5 pm EST Page 48 of 164